Cellulose fibers, typically cotton, are widely used because of their various advantages, e.g. hygroscopicity and good feel. However, cellulose fibers suffer the drawbacks of being susceptible to wrinkling and shrinking. To eliminate the drawbacks, a wide variety of substances have been used for treating cellulose fibers.
Urea-formaldehyde resins or their derivatives, e.g. glyoxal resins, have been extensively used as a cellulose fiber- treating agent, but they are defective. When used as such treating agent, formaldehyde is likely to remain in the cellulose fibers treated with the resin. Moreover, formaldehyde is notorious not only for its offensive odor but as a carcinogen. In treating cellulose fibers, formaldehyde may foul the work environment and may produce an adverse effect on consumers due to its presence in cellulose fiber articles.
From the viewpoint of improved safety, there is a tendency in recent years to urge a strict regulation on the use of carcinogenic formaldehyde or to tighten control of its use. Currently awaited is the .advent of epoch-making cellulose fibers having resistance to wrinkling and shrinking imparted without use of a formaldehyde derivative such as glyoxal.
U.S. Pat. No.3,526,048 to Roland et al proposed a polycarboxylic acid, e.g. 1,2,3,4-butanetetracarboxylic acid (hereinafter referred to as "BTC"), as a formaldehyde-free, effective cellulose fiber-treating agent. U.S. Pat. No.4,820,307 to Welch et al proposed alkali metal salts of hypophosphorous acid, phosphorous acid, polyphosphoric acid or the like as a catalyst for the esterification between the cellulose fibers and polycarboxylic acid.
BTC is commercially manufactured by oxidizing tetrahydrophthalic anhydride with nitric acid (CMC, 1990 year edition, Fine Chemical Yearbook, pp. 410, 1989). Welch et al reported that when cellulose fibers, e.g. white cotton, are treated according to U.S. Pat. Nos. 3,526,048 and 4,820,307 with BTC prepared by oxidation with nitric acid (hereinafter referred to as "nitric acid BTC"), the white cotton turned yellow (Text. Chem. Color, 25, 25 (1993)). Such coloring is undesirable whether on pigmented cotton or on white cotton. Consequently conventional nitric acid BTC remains to be improved in this respect for commercial use as a fiber-treating agent.